ORIGINAL ARTICLE Bamboo reinforced concrete: a critical review Hector Archila . Sebastian Kaminski . David Trujillo . Edwin Zea Escamilla . Kent A. Harries Received: 20 January 2018 / Accepted: 16 July 2018 / Published online: 19 July 2018 Ó The Author(s) 2018 Abstract The use of small diameter whole-culm (bars) and/or split bamboo (a.k.a. splints or round strips) has often been proposed as an alternative to relatively expensive reinforcing steel in reinforced concrete. The motivation for such replacement is typically cost—bamboo is readily available in many tropical and sub-tropical locations, whereas steel reinforcement is relatively more expensive—and more recently, the drive to find more sustainable alternatives in the construction industry. This review addresses such ‘bamboo-reinforced concrete’ and assesses its structural and environmental performance as an alternative to steel reinforced concrete. A prototype three bay portal frame, that would not be uncommon in regions of the world where bamboo- reinforced concrete may be considered, is used to illustrate bamboo reinforced concrete design and as a basis for a life cycle assessment of the same. The authors conclude that, although bamboo is a material with extraordinary mechanical properties, its use in bamboo-reinforced concrete is an ill-considered con- cept, having significant durability, strength and stiff- ness issues, and does not meet the environmentally friendly credentials often attributed to it. Keywords Bamboo Bamboo reinforcement Bamboo-reinforced concrete Concrete Durability Life cycle assessment 1 Introduction The mechanical properties of bamboo and its avail- ability in developing regions has led to its empirical use as reinforcement in concrete structures. The proposition of its widespread use as a sustainable alternative to steel in reinforced concrete structures, poses key questions to builders, engineers and researchers with regards to its structural capacity and compatibility, as well as constructability and sustain- ability issues. This paper discusses these issues, providing a holistic review of the literature in the field and a structural comparison between steel H. Archila K. A. Harries University of Bath, Bath, UK H. Archila Amphibia BASE, Bath, UK S. Kaminski Arup, London, UK D. Trujillo Coventry University, Coventry, UK E. Zea Escamilla Head of Sustainable Building Research, Center for Corporate Responsibility and Sustainability, University of Zurich, Zurich, Switzerland K. A. Harries (&) University of Pittsburgh, Pittsburgh, USA e-mail: [email protected]Materials and Structures (2018) 51:102 https://doi.org/10.1617/s11527-018-1228-6
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ORIGINAL ARTICLE
Bamboo reinforced concrete: a critical review
Hector Archila . Sebastian Kaminski . David Trujillo . Edwin Zea Escamilla .
Kent A. Harries
Received: 20 January 2018 / Accepted: 16 July 2018 / Published online: 19 July 2018
� The Author(s) 2018
Abstract The use of small diameter whole-culm
(bars) and/or split bamboo (a.k.a. splints or round
strips) has often been proposed as an alternative to
relatively expensive reinforcing steel in reinforced
concrete. The motivation for such replacement is
typically cost—bamboo is readily available in many
tropical and sub-tropical locations, whereas steel
reinforcement is relatively more expensive—and
more recently, the drive to find more sustainable
alternatives in the construction industry. This review
addresses such ‘bamboo-reinforced concrete’ and
assesses its structural and environmental performance
as an alternative to steel reinforced concrete. A
prototype three bay portal frame, that would not be
uncommon in regions of the world where bamboo-
reinforced concrete may be considered, is used to
illustrate bamboo reinforced concrete design and as a
basis for a life cycle assessment of the same. The
authors conclude that, although bamboo is a material
with extraordinary mechanical properties, its use in
bamboo-reinforced concrete is an ill-considered con-
cept, having significant durability, strength and stiff-
ness issues, and does not meet the environmentally
able and high-strength alternative material to timber
and, occasionally as a ‘strong-as-steel’ reinforcement
for concrete. The high rate of biomass production and
renewability of sustainably managed bamboo planta-
tions are undeniably key benefits of bamboo. Nonethe-
less, favourable comparison with steel, in terms of
strength, is not valid. In a dry state, bamboo charac-
teristic strengths are, at best, comparable to that of
high-grade hardwood—between 30 MPa (Oak) and
50 MPa (American White Oak) [1]. Bamboo is a
typically hollow, anisotropic, natural material with
high variability of physical and mechanical properties
across the section and along the culm. The density of
bamboo varies through the cross section (from the
inner culm wall to the outer), with typical values
ranging from 500 to 800 kg/m3. In longitudinal
tension-dominated failure modes, bamboo typically
exhibits a brittle behaviour. The variability of longi-
tudinal mechanical properties of bamboo are similar to
those of wood, having coefficients of variance
between 10 and 30% [2–4]. Due to the absence of
radial fibres, however, bamboo is particularly weak in
the direction perpendicular to the fibres, making it
especially susceptible to longitudinal shear and trans-
verse tension and compression failures. Steel, on the
other hand, is a man-made, isotropic and ductile
material having a density of 7800 kg/m3 and a tensile
yield strength of conventional reinforcing bars
between 400 and 550 MPa. Additionally, steel is
easily shaped to optimise its mechanical efficiency,
requiring relatively little material to resist loads in a
predictable manner. Such optimisation is not easily
accomplished with bamboo without substantial pro-
cessing, altering its properties and nature (e.g., Hebel
et al. [5]). The oft-repeated claim that bamboo is ‘the
green steel’ is founded in comparable-to-mild-steel
values of strength and specific modulus. Some tests of
small ‘clear’ (i.e., defect free) specimens of bamboo
have reported ultimate tensile strengths on the order of
250 MPa (e.g., Zhou et al. [6] and Lu et al. [7]).
However, such results are not representative of the
strength that can be mobilised in a full or partial culm:
characteristic strength on the order of 40 MPa and safe
working stress for design on the order of 16 MPa—
similar to hardwood timber [1]. The tensile modulus of
bamboo is on the order of 20 GPa [8], about 10% of
that of steel. The specific modulus—the ratio of elastic
modulus per unit density—for bamboo in the longi-
tudinal direction is approximately 25 9 106 m2/s2; a
value comparable to both steel and Douglas Fir.
However, unlike steel, the highly anisotropic nature of
bamboo results in a specific modulus in the transverse
or tangential directions barely a tenth of the longitu-
dinal value; values comparable to nylon and poly-
styrene. Thus, the mechanical properties of bamboo
and its appropriateness for structural applications are
often misunderstood. On the other hand, when com-
paring embodied energy and CO2 footprint during
manufacturing of bamboo and steel, a strong argument
can be made in favour of bamboo. The embodied
energy of medium carbon steel is about 29–35 MJ/kg,
while for bamboo culms this value is about 4–6 MJ/kg
[9]. Similarly, the carbon footprint of steel is signif-
icantly greater than that of bamboo, with
2.2–2.8 kgCO2/kg (equivalent kg of CO2 per kg of
material) for medium carbon steel [9] and
0.25 kgCO2/kg for bamboo [10].
2 Mechanics and behaviour of reinforced concrete
Reinforced concrete is a composite material. Design of
simple concrete cross sections is based on Bernoulli
beam theory simultaneously satisfying conditions of
equilibrium and strain compatibility. Equilibrium
requires only knowledge of the concrete and reinforc-
ing material constituent behaviours (modulus and
strength). Strain compatibility requires bond between
the concrete and reinforcing material to be maintained.
Bond of non-prestressed reinforcing elements (bars) to
concrete is primarily mechanical (through interlock
with the surrounding concrete). Plain (undeformed)
bars exhibit limited friction-induced bond. Any
chemical bond between bar and concrete is rapidly
102 Page 2 of 18 Materials and Structures (2018) 51:102
overcome and not considered to contribute to bond
capacity/behaviour.
2.1 Strength
In conventional steel-reinforced concrete design,
members are designed to be ‘under reinforced’ such
that the reinforcing steel yields prior to concrete
crushing. This ensures a ductile member response by
engaging the inherent ductility of the steel. This
behaviour also results in an inherent overstrength or
reserve capacity above the design requirement by
permitting plastic behaviour and redistribution of
internal stress to occur. Such behaviour allows mul-
tiple layers of steel reinforcement to be efficiently
engaged. For a brittle reinforcing material such as
bamboo or glass fibre reinforced polymer (GFRP),
reinforcement failure is unacceptable (resulting in
catastrophic failure of the member) and thus an ‘over-
reinforced’ design is prescribed by which limited
ductility is achieved through concrete crushing [11]. In
order to simultaneously satisfy equilibrium and strain
compatibility requires providing a force in the rein-
forcing element, T, at a strain that is ultimately limited
by concrete crushing strains. The force in the
reinforcing element is typically given as the product
of reinforcing bar area and stress in the bar,
T = A 9 f. While correct, this equation is more
accurately written T = A 9 eE where the stress in
the bar is in fact, the product of bar strain (e) and
modulus (E). Therefore, to achieve comparable
strength designs in steel and bamboo using only the
nominal tensile capacity, considerably more bamboo
area is required. The average tensile modulus of
Guadua angustifolia bamboo is on the order 20 GPa
[8], resulting in a modular ratio Esteel/Ebamboo = 10.
Since the tension resisted by the reinforcing material is
an issue of strength, a more conservative characteristic
value1 of tensile modulus falling between 7.5 and
13 GPa at 12% moisture content should be used in
design, resulting in a modular ratio as great as 27 [1].
Alternatively, larger strains may be developed to
achieve a comparable bar force; this leads to consid-
erations of serviceability: concrete crack control and
member deflection. In addition, because bamboo is
brittle an elastic distribution of stresses must be
adopted, therefore adding additional layers of bamboo
reinforcement provides progressively less benefit as
the stress level in each layer closer to the neutral axis is
progressively less.
2.2 Serviceability and minimum reinforcement
Serviceability of concrete is typically considered in
terms of member deflections and concrete crack
control. Both are affected by the axial stiffness (AE)
of the reinforcing material. Assuming concrete is
cracked (if it is not, it may be considered to be
unreinforced), crack width, and therefore curvature
and deflection, is a function of the axial stiffness of the
reinforcing bar bridging the crack. Once again, bar
area of a softer reinforcing material must be increased
based on the modular ratio to achieve designs com-
parable to steel-reinforced concrete.
Minimum reinforcement is required for reinforced
concrete members to ensure that they do not fail in a
brittle manner immediately upon cracking. Conceptu-
ally, steel-reinforced concrete is designed to ensure
that the nominal moment capacity exceeds 120% of
the cracking capacity: Mn C 1.2Mcr (ACI 318-14).
Additionally, minimum reinforcement is intended to
provide crack control; that is, once a section is
cracked, there is sufficient reinforcement to permit
the development of additional cracks rather than all
deformation being concentrated at a single initial
crack. For steel-reinforced concrete, adequate crack
control is achieved providing a reinforcing ratio of
least 0.33% (ACI 318-14). Based on a typical nominal
modular ratio (serviceability requirements will typi-
cally consider mean, rather than characteristic mod-
uli), this implies requiring more than 3.5% bonded
bamboo reinforcement to provide adequate crack
control. Furthermore, this assumption assumes that
the bond characteristics between reinforcing material
and concrete are similar. If bond behaviour is poor or
limited, considerably more bamboo reinforcing mate-
rial is required.
It is informative to consider the case of GFRP-
reinforced concrete [11]. GFRP bars have a modular
ratio Esteel/EGFRP on the order of 5. Design of such
members is most often governed by serviceability
considerations. Furthermore, to result in ‘practical’
designs, serviceability requirements for GFRP-rein-
forced concrete are often relaxed from those for steel-
1 For bamboo culms, characteristic values are most often cited
as the 5th percentile value determined with 75% confidence
[12].
Materials and Structures (2018) 51:102 Page 3 of 18 102
reinforced concrete. In particular, achieving accept-
able crack control in GFRP-reinforced members often
requires more reinforcement than is required for
strength. These issues would be exacerbated using
bamboo whose modular ratio is greater than 10. In
fact, crack control using bamboo may be even more
inefficient since the modulus of the bamboo will
typically be less than that of the surrounding concrete.
2.3 Bond and development
Integral to the foregoing discussion is the assumption
of ‘perfect bond’ permitting force transfer between the
reinforcing material and the surrounding concrete. To
transfer force adequately, there must be a sufficient
length of bar, known as the development length, over
which the force is transferred from the concrete to the
reinforcing bar. Bond force is developed by chemical
adhesion, friction, and mechanical interlock between
bar deformations and the surrounding concrete.
Chemical adhesion is small, rapidly overcome and
therefore neglected. The remaining components form
a resultant stress that can be further broken into
longitudinal (friction) and radial components. For
deformed bars, mechanical interlock is the primary
method of bond force transfer. For anisotropic mate-
rials, the radial component is reduced due to the
greater compliance of the bar in the transverse
direction. This may also lead to a second-order
reduction in friction. If round bamboo or splints are
used, there is little in the way of deformations to
provide mechanical interlock. Thus, bond behaviour
of bamboo reinforcement is anticipated to be more
analogous to smooth bar than deformed bar develop-
ment; relying mostly on friction to affect bond.
3 Bamboo-reinforced concrete
Published accounts indicate that the use of bamboo to
reinforce concrete structures dates back a century in
Southeast Asia. Early experimental studies of bam-
boo-reinforced concrete were conducted at MIT by
Chow [13], in Germany [14], Italy [15], the United
States [16], Smith and Saucier [17] and Colombia
[18]. These studies used either bamboo bars (whole-
culms of small diameter) or splints (semi-round
strips).
Much early interest in bamboo-reinforced concrete
is attributed to the US Navy and their interest in rapid
[re-]construction in Southeast Asia following the
Second World War. Research conducted by Glenn
[16] on bamboo-reinforced concrete, financed by the
US War Production Board, included mechanical tests
and the construction of experimental buildings. Glenn
produced a set of conclusions from the test results
obtained, as well as design and construction principles
for the use of bamboo canes and splints as reinforce-
ment in concrete. Glen highlighted issues such as
(a) high deflection, low ductility and early brittle
failure of the bamboo reinforced concrete beams under
load; (b) their reduced ultimate load capacity when
compared to steel-reinforced elements; (c) bonding
issues associated with excessive cracking and swelling
of bamboo; and, (d) the need for using asphalt
emulsions. Glenn advises use of a bamboo tensile
stress of 34–41 MPa based on maximum stress values
of 55–69 MPa for concrete beams with 3–4% bamboo
reinforcement. Finally, an allowable bamboo tensile
stress between 20 and 28 MPa for reinforced elements
is recommended by Glenn in order to keep the
deflection of the beam below 1/360 of the span.
Two later studies that report ‘design methodolo-
gies’ stand out. Brink and Rush [19] promulgate an
allowable stress approach for designing bamboo-
reinforced concrete comparable to the contemporary
ACI 318 [20] approach for steel-reinforced concrete.
Brink and Rush recommend an allowable bamboo
tensile stress of 28 MPa based on an ultimate capacity
of 124 MPa and a bond strength of 0.34 MPa. For
serviceability requirements, they recommend a bam-
boo modulus of elasticity of 17.2 GPa.
Geymayer and Cox [21], on the other hand,
recommend a hybrid design approach in which a
bamboo-reinforced concrete flexural element is
designed as an unreinforced concrete member with a
maximum tensile stress of 0:67pf 0c (MPa units). To
this, 3–4% bamboo reinforcement is added resulting
in, they claim, a factor of safety on the order of 2–2.5.
A more refined analysis may be conducted using a
recommended allowable bamboo stress of 34 MPa
and modulus of 13.8 GPa for tension reinforcement
and 8.6 GPa for flexural reinforcement. Geymayer and
Cox recognise the unique and limited bond behaviour
of bamboo and recommend that bond strength be
44 N/mm of reinforcing ‘bar’ circumference and that
102 Page 4 of 18 Materials and Structures (2018) 51:102
the embedment provided must exceed 305 mm. This is
a maximum bond stress of about 0.15 MPa. Geymayer
and Cox based their study on Arundinaria tecta, a
species of bamboo native to the Southeast United
States.
Using either allowable stress-based approach, bond
capacity will always control design. As a basis of
comparison, a 25 mm diameter bamboo reinforcing
bar embedded 305 mm can develop only between
3.5 kN [21] and 8.4 kN [19]. By contrast, a 9.5 mm
diameter steel reinforcing bar in the same conditions
can develop 29.4 kN.
A number of research papers describing bamboo-
reinforced flexural members confirm the basic premise
of the design methodology proposed by Geymayer and
Cox [21]. Optimal ratios of longitudinal bamboo
reinforcement range from 3 to 5% from which the
capacity of an otherwise unreinforced concrete beam
is increased at least 2.5 times [22–27]. It is recom-
mended that design capacity be limited to the unre-
inforced section cracking moment, Mcr, which, for a
bamboo-reinforced section, should lead to a ‘factor of
safety’ against cracking of 2 and against failure of 7
[23]. Although specific investigation of bond was not
included in these studies, recommendations for the use
of bamboo splint reinforcement include the require-
ment for two coats of bituminous paint with sand
broadcast onto the top coat [23]. This is a procedure
similar to that applied to bamboo splints by Ghavami
[28], in which the author roughened the surface of
bamboo before applying an initial coat of bituminous
paint with sand and subsequently wrapped a 1.5 mm
wire around the splints before applying a second coat.
In unrelated studies, Ghavami [29], Agarwal et al.
[30] and Sevalia et al. [31] demonstrate the importance
of providing at least minimum bamboo reinforcement
and appropriate surface treatment to enhance bond.
Ghavami [29] found that beams with a 3% ratio of split
bamboo reinforcement had four times the ultimate
capacity of comparable unreinforced concrete beams.
In the latter two studies, the authors report that
bamboo-reinforced concrete with splints having no
bond enhancement and a reinforcing ratio of approx-
imately 1.4%, offer no improvement over the
behaviour of unreinforced concrete. Similarly, bam-
boo-reinforced slabs having a reinforcement ratio of
only 0.5% developed a single large crack and exhib-
ited significant reinforcement slip [32].
Two studies, Terai and Minami [33] and Leela-
tanon et al. [34], considered bamboo reinforcement for
axial compression carrying members. These studies
tested concentrically loaded column stubs having
height to breadth ratios of 2 and 2.5, respectively. As
should be expected from such short specimens, axial
capacity may be approximated using transformed
sections analysis and is improved in the presence of
transverse confinement. No distinct difference
between steel or bamboo-reinforced behaviour was
evident in either experimental programme. Due to the
short test specimen geometry, these tests have no
reliance on bond to the concrete.
Ghavami [29] carried out an exploratory study on
2 m high concrete columns having 200 mm square
cross-sections. These were reinforced with longitudi-
nally-oriented bamboo splints having bond-enhancing
surface treatment and were confined with steel
stirrups. Ghavami remarks that 3% bamboo reinforce-
ment in concrete columns was an ideal ratio to comply
with Brazilian building regulations, but does not
provide any values of ultimate strength or further
details.
3.1 Bond and development
Agarwal et al. [30] showed the significant beneficial
effects of ‘treating’ bamboo splints with commercial
epoxy-based adhesives in order to enhance bond. They
reported average bond stresses (from pull-out tests) on
the order of 0.13 MPa for plain bamboo splints (a
value echoing the recommendation of Geymayer and
Cox [21]) and values as high as 0.59 MPa (350%
increase) when Sikadur 32 adhesive was used to coat
the splints. This behaviour translated to improved
flexural response. Similarly, Ghavami [28] reports a
430% increase in the value of bond strength for
Sikadur 32-coated bamboo splints embedded in con-
crete, when compared to uncoated splints; bond
strength values were: 2.75 and 0.52 MPa, respec-
tively. Ghavami also conducted tests with an asphalt
(Negrolin) and sand coat which resulted in a bond
strength of 0.73 MPa (Fig. 1). Agarawal et al. report
that a bamboo reinforcing ratio of 8% was necessary to
result in flexural behaviour similar to that of a steel-
reinforced concrete member having a reinforcing ratio
0.89% (with a reported modular ratio, Esteel/Ebamboo-
= 8.3). Bamboo splint reinforcement coated in
Sikadur 32 required a reinforcing ratio of only 1.4%
Materials and Structures (2018) 51:102 Page 5 of 18 102
to achieve behaviour similar to that steel; implying a
470% improvement in behaviour when the splints
were coated.
Terai and Minami [32] report pull-out bond tests of
round bamboo samples having a variety of synthetic
resin and synthetic rubber surface treatments.
Untreated bond stress capacity is reported to be
0.66 MPa and treatments increased this to values
ranging up to 1.34 MPa. In the same test program, the
bond capacity of deformed steel bar was reported as
2.43 MPa.
More realistically, Geymayer and Cox [21] and
Sakaray et al. [35] report pull-out bond tests of splints
and round culms, respectively, having varying embed-
ment lengths. Both studies conclude that the average
bond stress decreases as the embedment length
increases, and that this decrease is significantly more
pronounced than is observed in [isotropic] steel
reinforcing bars. Such a reduction can be explained
by the greater effects of shear lag and the poor
transverse material characteristics of the anisotropic
bamboo. As seen in Fig. 1, bamboo splints, which
have no pronounced deformations (thus relying mostly
on friction to transfer stress), exhibit a lower bond
stress than round culms for which the nodal protru-
sions provide some degree of mechanical interlock.
Geymayer and Cox concluded that bamboo splints had
an effective bond length, beyond which further
increases in embedded length had no effect on
available capacity; from this they established their
recommendation that bond strength be 44 N/mm of
reinforcing ‘bar’ circumference and that the embed-
ment provided must exceed 305 mm.
The presence of silica (SiO2) in bamboo could
contribute to a pozzolanic reaction, increasing the
amount of calcium silicate hydrates (CSH) through
reaction with Ca(OH)2 during hydration of Portland
cement, that improves binding with concrete. How-
ever, the silica in bamboo occurs primarily in the
epidermis (in a cellular level) and must be exposed to
the concrete for the pozzolanic reaction to take place
[36]. Therefore, when using bamboo in the form of
culms or splints, additional pozzolanic activity is
doubtful and is unlikely to contribute in any mean-
ingful way to bamboo-concrete bond.
All known studies that address bond of bamboo in
concrete identify shrinkage of untreated, green or pre-
soaked bamboo, and swelling cycles resulting from
variations in moisture in the concrete as being
detrimental to bond. As a result, most studies recom-
mend coating the bamboo in a moisture barrier,
provided the coating does not result in a lubricating
effect thereby, itself degrading the bond. On the other
hand, sealing inadequately seasoned bamboo into a
watertight environment has the potential to exacerbate
decay. Finally, in practice, it is difficult to achieve a
reliable and durable condition of water tightness.
0.0
0.5
1.0
1.5
2.0
2.5
3.0
0 100 200 300 400 500 600 700
aver
age
bond
stre
ss o
ver e
mbe
dmen
t len
gth,
MPa
pull-out embedment length, mm
round culms no surface treatment (Sakaray et al. 2012)splints no surface treatment (Geymayer and Cox 1970)splints with no node (Ghavami 1995)splints with node (Ghavami 1995)splints (Ararwal et al. 2014)round culms (Terai and Minami 2012)
arrows indicate improvementin bond capacity resultingfrom surface treatment
Fig. 1 Variation of bond
stress with embedded length
and the effects of surface
treatment
102 Page 6 of 18 Materials and Structures (2018) 51:102
A common practice is to coat the bamboo in an
epoxy or polyester resin and broadcast sand onto this
to enhance bond characteristics; however, due to
bamboo’s hygroscopic nature, variations in bamboo
moisture content (MC), and relative humidity (RH),
swelling or contraction of the material depending on
moisture absorption and loss can occur. This can lead
to labour and energy intensive, and potentially
expensive treatments that defeat the purpose of using
an inexpensive and locally available material. For
example, Javadian et al. [37] report a maximum bond
strength comparable to that of steel reinforcing bars,
3.65 MPa, for highly processed composite bamboo
splints. To achieve this high bond stress, the splits
were dried below 10% moisture content, heat-treated
under pressure (to increase the density of bamboo) and
coated using a water-based epoxy and fine sand.
Overall, research into cementitious and polymeric
composites using bamboo and other natural materials
as reinforcement, highlight common issues such as
biodegradability, manufacturability and thermal com-
patibility of the bamboo and matrix material [29, 38].
A final issue potentially affecting bond performance of
bamboo is the coefficient of thermal expansion (CTE)
which is a) affected by moisture content; and b) is as
much as five times less than that of concrete or steel in
the longitudinal direction, but two times greater than
this value in the transverse direction. The reported
CTE in the longitudinal direction for bamboo ranges
between 2.5 and 10 9 10-6/C; transverse CTE is
approximately an order of magnitude greater [9].
3.2 Durability of bamboo reinforcement
in concrete
Durability of bamboo is closely related to its natural
composition. As with other lignocellulosic materials,
bamboo consists of cellulose, hemicellulose and
lignin. The chemistry of these components in bamboo
changes with age (e.g., when the plants reaches its
mature state) and/or after harvesting, which triggers a
process of cell death and tissue decay. Significant
statistical correlation between changes in chemical
composition, age and density in Phyllostachys pub-
escens and Gigantochloa scortechinii have been
reported by Li et al. [39] and Hisham et al. [40],
respectively.
There are few known studies specifically address-
ing the durability of bamboo embedded in concrete.
Nonetheless, there is considerable literature address-
ing the durability and treatment of different biomass
materials (occasionally including bamboo) in cemen-
titious materials. Gram [41] represents perhaps the
first significant study in this regard and Vo and Navard
[42] and Pacheco-Torgal and Jalali [43] provide recent
and very thorough reviews. Most extant studies focus
on ‘fibre-reinforcement’ or the inclusion of pulp
materials in a cementitious composite. In this review,
the authors have addressed only those durability issues
believed to be relevant to bamboo-reinforced concrete.
Readers are directed to the review articles noted for a
discussion of other related durability issues.
Portland cement concrete is a highly alkali envi-
ronment. The pH of pore water in Portland cement
concrete typically exceeds 12. This provides a passi-
vating environment for embedded steel reinforce-
ment—effectively mitigating the potential for steel
corrosion provided the pH remains higher than 10
[44]. In contrast, alkali treatments are often used to
break-down the cell structure of lignocellulosic mate-
rials such as wood, hemp, flax and bamboo [45] in
order to retrieve, expose or treat their fibres. Such
treatment may improve surface roughness (so called
fibre sizing) to improve bond with polymeric resins in
composite materials but are clearly undesirable in the
case of bamboo bars used in bamboo-reinforced
concrete. Hosoda [46] reports a 50% loss of bamboo
tensile capacity following 1-year conditioning in a
high alkali water bath; after 3 years, the bamboo
retained only 30% of its initial strength. Hemicellulose
and water soluble extractives (the latter should gen-
erally not be present in treated bamboo culms) are
reactive with calcium hydroxide (Ca(OH)2) present in
cement paste [47–50] leading to crystallisation of lime
in the biomass pores [43]. Lignin is soluble in hot
alkali environments [41] as is the case during cement
hydration, and potentially when the concrete is
exposed to direct sunlight in a tropical environment.
Reducing alkalinity whether using ternary cements
[51] or through carbonation [52] were found to only
partially mitigate the degradation of biomass. Ligno-
cellulosic materials in hydrated cement are also
embrittled by mineralisation associated with cations
(primarily Ca2?) in the concrete pore water [53].
Water absorption is a critical durability concern for
biomass of any kind embedded in a cementitious
matrix [43]. Water absorption and hygrothermal
cycling result in essentially continuous volumetric
Materials and Structures (2018) 51:102 Page 7 of 18 102
change of the embedded biomass leading to interfacial
damage and micro- and macro-cracking. These effects
increase permeability, driving the deleterious pro-
cesses described previously.
Biological attack is arguably the most critical
concern for bamboo. When compared to wood there
are certain factors that make bamboo more prone to
decay, including: (a) its thin-walled geometry (making
decay more significant in terms of reduction in
member capacity), (b) its high starch content, and
(c) the absence of decay-resistant compounds such as
those found in some hardwood species such as Teak
and Ipe [3, 54, 55]. There are two causes of biological
decay in bamboo: insect (such as beetles and termites)
and fungal attack (rot). Like timber [3, 56], four
measures are required to protect bamboo from insect
and fungal attack: (a) season the bamboo; (b) treat the
entire through-thickness with chemicals; (c) keep
bamboo dry and able to ‘breath’ throughout its life;
and, (d) keep bamboo out of reach of termites.
Embedment in concrete is not believed to be
sufficient to protect bamboo from insect—especially
termite—attack. Termites can pass into cracks as
small as 0.8 mm [57]. Bamboo-reinforced concrete is
likely to exhibit such cracks from temperature,
shrinkage and/or load effects. Thus, bamboo rein-
forcement requires chemical treatment through its
entire wall thickness to mitigate insect attack [55, 58].
Fungal attack (rot) requires aerobic conditions and
a moisture content typically exceeding 20% [59].
Bamboo that is fully or partially embedded in concrete
is vulnerable to rot because concrete (or mortar) is
porous and moisture is easily transported through
capillary action [60] and through existing cracks.
Additionally, embedment in concrete is likely to
prevent moisture that is present as a result of ingress,
from rapidly evaporating or dispersing resulting in an
increment in the moisture content of the bamboo.
Surface or ‘paint-on’ treatments are generally not
considered to provide sufficient protection against rot
in timber [3, 56, 59] or bamboo [61]. To the authors’
knowledge no comprehensive tests have been con-
ducted to specifically assess the likelihood of bamboo
decay when completely embedded in concrete. Except
in cases in which the concrete remains dry throughout
its service life, decay is possible even when the
bamboo is coated in a bituminous or epoxy coating.
The issues of bamboo reinforcement degradation
are aggravated by the fact that such damage will
remain unseen. For example, corrosion of steel
reinforcement occurs over years or decades and results
in expansion of the steel reinforcement, leading to
cracking, staining and spalling of the cover concrete
thereby providing a visual ‘warning’ before the
corrosion has become a safety–critical issue. How-
ever, in some environments bamboo could decay
rapidly and degrade without providing an indication of
damage at the concrete surface.
4 Example: three bay portal frame
In order to illustrate bamboo-reinforced concrete and
contrast this with steel-reinforced concrete the first
storey of a three bay, two story portal frame prototype
is considered (Fig. 2a). The frame is 2.5 m tall and
each bay spans 4.3 m. Such a frame would not be
uncommon in regions of the world where bamboo-
reinforced concrete may be considered (Fig. 2b). The
details of the steel-reinforced concrete prototype are
selected (Fig. 3) and its nominal (i.e., unfactored)
gravity load carrying capacity determined post priori
based on the provisions of ACI 318 [62]. The bamboo-
reinforced alternative is designed for the same gravity
load and frame dimensions. In this way, the frames are
identical functional units—they carry the same nom-
inal loads over the same spans. For the sake of
example, it was assumed that the frame is located in a
structure also having infilled walls, thus the frame
considered is not required to carry lateral load.
The following assumptions were made:
1. Concrete compressive strength, f 0c ¼ 21 MPa
2. Concrete modulus of rupture, fr ¼ 0:6pf 0c ¼
2:75 MPa
3. Reinforcing steel yield strength, fy = 276 MPa
(such lower grade steel reinforcement is more
typical in regions that may consider the use
bamboo reinforced concrete)
4. Moments and shears were determined by ACI 318
§6.5 simplified analysis; as a result, the critical
section is negative flexure over the first interior
support where the design moment is 0.1wL2 and
the design shear is 0.58wL, in which w is the
uniformly distributed gravity load and L is the
beam span.
5. 25 mm clear cover for all members.
102 Page 8 of 18 Materials and Structures (2018) 51:102
6. Centre-to-centre spacing of bamboo bars must be
at least 3 9 culm diameter to permit adequate
consolidation of concrete.
The beam section is 300 9 200 mm (height (h) 9
width (b)) having 2–15 M bars (area of single
bar, Ab = 200 mm2) top and bottom. The columns
are 200 mm square having 4–15 M bars. 10 M
(Ab = 100 mm2) transverse hoops spaced at
s = 250 mm are provided in both the beam and
column sections. Although both beams and columns
are ‘doubly reinforced’, their moment capacity was
assessed as though they were only singly reinforced.
The depth to the primary tension reinforcement for the